1. Field of the Invention
The present invention relates to the field of earth boring tools, and in particular to the operation and apparatus relating to downhole tool operation such as core catchers.
2. Description of the Prior Art
Coring is in common practice in the field of petroleum exploration and it involves a practice wherein a drill string, comprised of sections of outer tube, which ultimately terminate in a coring bit, cut a cylindrically shaped core segment from the rock formation. The core is then broken off and brought to the surface for examination. However, it is not uncommon to encounter formations which are unconsolidated, fragmented or loose. Therefore the core, after being cut, generally will not retain a rigid configuration but must be held and retained within an inner tube which is concentrically disposed within the outer tube of the drill string. Furthermore, not only must a core catcher be activated to break the lower portion of the core from the underlying rock formation from which it was cut, but in many cases the rock formation is so unconsolidated, as in the case of oil-sand, water-sand, or loose debris, that a full closure core catcher must be used to positively seal the bottom of the inner tube if the core material is to be retained within the inner tube as the drill string is lifted from the borehole. The best form of such full closure catchers are manipulatively operated from the surface at the end of the coring operation and prior to retrieval of the core sample. It thus becomes desirable to have some type of means within the drill string for performing these and other operations which may become necessary during coring operations, or generally within drilling operations.
Therefore, what is needed is an apparatus for manipulating the core catcher within a drill string, such as by lifting the inner tube to uncover the core catcher, to retain the cored material during coring operations. The apparatus must be rugged, simple in operation, reliable within the drilling environment and, preferably, automatically perform its operation once selectively initiated by the platform operator without dependence on gravity, friction with the core or any other aspect of the downhole operation being implemented.